1. Field of the Invention
The present invention relates to polymeric positive temperature coefficient (PPTC) resistance electrical circuit protection devices adapted to surface mount technology. More particularly, the present invention relates to a miniature surface mount integrated component having a monolithic multi-layer package combining at least one PPTC element and at least one heat-generating semiconductor element in a manner providing improved heat transfer characteristics, the component being formed using printed circuit board construction techniques.
2. Introduction to the Invention
PTC devices are well known. Particularly useful devices contain PTC elements composed of a PTC conductive polymer, i.e. a composition comprising an organic polymer and, dispersed or otherwise distributed therein, a particulate conductive filler, e.g. carbon black, or a metal or a conductive metal compound. Such devices are referred to herein as polymer PTC, or PPTC resistors or resistive devices. Other PTC materials are also known, e.g. doped ceramics, but are not as generally useful as PTC conductive polymer, in particular because they have higher non-operating, quiescent resistivities.
As used herein, the term “PTC” is used to mean a composition of matter which has an R14 value of at least 2.5 and/or an R100 value of at least 10, and it is preferred that the composition should have an R30 value of at least 6, where R14 is the ratio of the resistivities at the end and the beginning of a 14° C. range, R100 is the ratio of the resistivities at the end and the beginning of a 100° C. range, and R30 is the ratio of the resistivities at the end and the beginning of a 30° C. range. Generally the compositions used in devices of the present invention show increases in resistivity that are much greater than those minimum values.
PTC resistive devices can be used in a number of different ways, and are particularly useful in circuit protection applications, in which they function as remotely resettable fuses to protect electrical components from excessive currents and/or temperatures. Components which can be protected in this way include motors, batteries, battery chargers, loudspeakers, wiring harnesses in automobiles, telecommunications equipment and circuits, and other electrical and electronic components, circuits and devices. The use of PPTC resistive elements, components and devices in this way has grown rapidly over recent years, and continues to increase.
Suitable conductive polymer compositions and elements, and methods for producing the same, are disclosed for example in U.S. Pat. No. 4,237,441 (van Konynenburg et al.), U.S. Pat. No. 4,545,926 (Fouts et al.), U.S. Pat. No. 4,724,417 (Au et al.), U.S. Pat. No. 4,774,024 (Deep et al.), U.S. Pat. No. 4,935,156 (van Konynenburg et al.), U.S. Pat. No. 5,049,850 (Evans et al.), U.S. Pat. No. 5,250,228 (Baigrie et al.), U.S. Pat. No. 5,378,407 (Chandler et al.), U.S. Pat. No. 5,451,919 (Chu et al.), U.S. Pat. No. 5,747,147 (Wartenberg et al.) and U.S. Pat. No. 6,130,597 (Toth et al.), the disclosures of which are incorporated herein by reference.
It is known to provide PPTC resistor devices or elements in protective electrical connection and thermal contact with electronic components such as zener diodes, metal oxide semiconductor field effect transistors (MOSFETs), and more complex integrated circuits forming voltage/current regulators, as exemplified by the teachings and disclosures set forth in commonly assigned U.S. Pat. No. 6,518,731 (Thomas et al.) (particularly FIGS. 45 to 47), the disclosure of which is incorporated herein by reference. Also, see for example U.S. Pat. No. 3,708,720 (Whitney et al.) and U.S. Pat. No. 6,700,766 (Sato). These exemplary patents do not show fully integrated surface mounted components made by using low cost printed circuit board manufacturing techniques in which the heat-generating element, such as a semiconductor chip, is connected to a printed circuit board via one or more contact pads provided by the PPTC carrier structure.
Circuit elements comprising PPTC resistive elements have been formed in accordance with printed circuit board (PCB) construction techniques. In these prior approaches, PPTC plaque(s) serves as a material layer(s) and is incorporated into a PCB construction by lamination using PCB lamination processes and materials in order to form circuitry layers for external mounting of other discrete passive or active electrical components. Examples of circuit protection devices including PPTC-PCB laminar constructions include U.S. Pat. No. 6,300,859 (Myong et al.) and U.S. Pat. No. 6,392,528 (Myong), the disclosures of which are incorporated herein by reference.
Some passive electrical components can be embedded layers in the PPTC-PCB construction. These embedded layers can be resistors, capacitors, and inductor elements. Plated vias (whether through-hole, blind, buried, isolated, etc.) enable appropriate electrical connections to be made from layer to layer.
It is known to provide a multi-layer PPTC resistive device. One reason for providing multi-layer devices is to provide increased current handling capabilities within a resistive device by providing increased surface area contact between the PPTC plaque and current-carrying electrode layers without increasing the “footprint” of the device. The device may have multiple conductive layers as an integrated construction, as suggested by U.S. Pat. No. 6,236,302 (Barrett et al.); or, the device may be formed by stacking separately formed PPTC resistive elements, as suggested by published U.S. Patent Application No. US2002/0125982 (Swensen et al.).
Multi-layer surface mount PPTC resistor fabrication methods and resultant electrical components are described in commonly assigned U.S. Pat. No. 6,640,420 (Hetherton et al.). In particular, FIGS. 16 through 19 illustrate a three-contact surface mount composite device having two electrical elements in thermal contact and electrically connected in a series arrangement. A related published U.S. Patent Application No. US2002/0162214A1 (Hetherton et al.) includes a stacked PPTC surface mount device having upper face contact pads for receiving and connecting additional elements, such as one or more semiconductor devices. The disclosures of this patent and published application are incorporated herein by reference.
Further, it has been proposed by U.S. Pat. No. 6,489,879 (Singh et al.) to bond a semiconductor die forming a heating element to a PPTC lead frame using thermally conductive epoxy. However, the resultant assembly comprises and requires a structurally complex multi-contact lead carrier structure that is not formed in accordance with low cost printed circuit board manufacturing techniques. Also, once the completed device is surface-mounted to a printed circuit board, it may not be possible to inspect visually the integrity of connection of the interior contact leads of the semiconductor device to the underlying printed circuit board.
Separate from the use of PPTC plaques and laminar constructions, it has been suggested to sandwich a semiconductor diode between two printed circuit board layers in order to realize a surface-mountable diode component, as suggested by U.S. Pat. No. 5,994,167 (Tai et al.). However, the arrangement disclosed therein does not address or solve any of the thermo-electric problems solved by the present invention.
A hitherto unsolved need has remained for a miniature surface mount integrated component having a monolithic planar package combining a heating element carrier including at least one PPTC element and at least one heat-generating electrical element such as a semiconductor die in a manner providing improved heat transfer characteristics, the heating element carrier being formed by using low cost printed circuit board construction techniques.